| ... |
The overview shows N9, N8
and N7 are preset. This results in a frequency range of 384.0000 MHz (all
dipswitches open) - 511.9875 MHz (all dipswitches closed) in 12.5 kHz steps.
Why this very wide frequency
range? This way you can choose where you want your local oscillator above
or beneath the frequency your working on. When this Nokia is used in the
23 cm band with a tripler (also on my homepage), you need a flexible controller
with a wide frequency range.
The controller (Schematics
controller in PDF) uses four shift registers, type 74HC165. 8 bits
parallel into every 74HC165. With 4 of these shift registers a bitstream
of 32 bits can be made. More than enough for this application. The first
13 bits are not used and are preset to 0. Bits 14 until 18 are C1, C2,
N9, N8, and N7 and are preset, as described before. The remaining 14 bits
are adjustable: 7 bits for the MHz, 7 bits for 12.5 kHz.
U6A and U6B make a SR-flipflop.
As soon as the Nokia is connected to a power supply unit, this flipflop
will start counter U5. Databits are now sent to the pll. When this is completed,
the flipflop is reset via U6C and counter U5 stops. This all takes place
within 1 second. The rest of the time, flipflop, counter and shif registers
don't do anything. Only the first second after " starting up" your Nokia.
U7A is used as an inverter.
When the packet modem wants the transceiver to transmit, ptt is drawn to
ground. The output of U7A will then go high and transistor Q1 becomes active.
The voltage on the emitter of Q7 is now available for the pa and the pinswitch.
Q7B is also used as an inverter.
This voltage is used to prevent the tx-oscillator from oscillating during
reception. An idea from PA3EKO, and it shall be discussed later in this
document.
|
... |
 |
|
| ... |
A
pinswitch is used because it's a fast rf switch, reliable and it doesn't
make annoying clicking sounds like a relay. Mitsubishi makes pinswitch
modules for 70 cm, but they are expensive. Furthermore, they can't be repaired
when something should go wrong.
Schematics
pinswitch in PDF
It
works as follows: during reception no voltage is applied. The diodes will
not conduct and have a high impedance. An rf signal arrives from the antenna.
On its right side, it will experience the high impedance of D5, a barrier.
The signal can travel to the left side, via the two coaxial lines, to the
receiver. How about tx? Voltage is applied and all diodes will conduct
and have a low impedance. Rf power from the power amplifier goes via D5
and C1 directly to the antenna. Why does the rf power doesn't go directly
into the receiver? Diodes D1, D2, D3 and D4 conduct and can be seen as
shortage to ground. These low impedances are transformed by the coaxial
transmission line into a high impedance, because the line has an electric
length of a quarter of a wavelength. So the rf power from the pa experiences
a high impedance and will not reach the receiver. By adding an extra quarter
wave line with two diodes, extra separation between pa and rx is created.
|
... |
 |
| ... |
... |
The
top side of the double sided pcb has all the tracks, the bottom side is
a ground plane. Don't forget to drill all the holes and solder the connections
between top and bottom side.
The
coaxial cable for the antenna port was removed from the original Nokia
duplexfilter. Connectors for tx and rx are SMB. Don't forget to remove
copper around the center pin of J1 on the bottom side of the pcb.
|
... |
|
 |
| ... |
... |
The
official Nokia MD59LS service doc is not necessary. For those who do have
it, I'll use references according to the original documentation, like L19,
L23, etc.
Open
the Nokia. On one side you find duplexfilter, audio pcb and processor pcb.
Remove these three. The two compartments will be used for the new controller
and the pinswitch. The other side of the Nokia: Power amplifier, synthesizer
and receiver module.
|
... |
|
| ... |
On one end of the rx module
you'll find a brown connector with 5 pins. Pin 1 [10]
is close to the potentiometer. Cut the track on the bottom side that goes
to this pin [21]. Now
make a connection [20]
from pin the earlier mentioned pin 1 to pin 8 of the demodulator TDA1576.
Replace the hexlixfilter [09]
by a 70 cm filter, for example the pin compatible 252MX1549A. No tuning
needed. This completes the modification of the receiver.
... |
... |
... |
|
 |
| ... |
 |
|
 |
| ... |
 |
|
| ... |
... |
Pin 1 of the 145156 is grounded
via a 3R9 smd resistor. Remove this smd resistor and place it back in such
a way that pin 1 is connected to pin 5 of the 145156 via the 3R9 smd resistor.
Remove the smd resistor on pin 19 of the 145156. Pin 19 is not connected
now. Make a connection between pin 19 of the 145156 and pin 3 of the 7474.
Pin 1 [07] of the brown
connector with 7 pins (pin 1 closest to the pa) has on the bottom side
an smd C and smd R to ground. Remove both. Seen from pin 1 of the brown
connector, the next part is a plastic C [06],
directly beside the square adjustable inductor [06].
Shortcut this condensator. Replace the original 31.4 MHz crystal [06]
by a 21.4 MHz standard crystal. If it's difficult tot get it working on
21.4 MHz exactly, try using shortcutting the square adjustable inductor
[06] on the bottom
side of the pcb. This works fine with low cost 21.4 MHz crystals.
|
... |
|
| ... |
C38 [16]
[18] is a 1p8 smd condensator.
It's the coupling C between varicap and the frequency determining LC circuit.
By increasing this C, not only the frequency goes down but also the caption
range of the pll goes up. Place 2p2 smd on top of the 1p8 condensator,
which results in a new 4 pF coupling C.
Beside the 12.8 MHz TCO
is a 78L05 voltage stabilizer which sometimes oscillates spontaneously
[08]. Place a 10uF
elco on the output of the 78L05 to ground, as close as possible tot the
78L05. Unwanted oscillations result in loud noise on the local oscillator
signal.
|
... |
... |
|
 |
|
|
| ... |
... |
Schematiscs
fast-ptt-mod in PDF
The PA3EKO-fast-ptt-mod:
Solder a diode 1N4148 with its cathode to the emitter of smd transistor
Q6[17] on the bottom
side of the pcb. Drill a hole at the emitter [19].
Diode 1N4148 [11] is
placed on the top side with its cathode through the drillhole, after removing
copper around the hole. Connect a 1 nF ceramic condensator from the anode
of the 1N4148 to ground [11].
On the top side, near the brown 7 pin connector, you'll find 2 inductors
which look like resistors, L19 [13]
and L23 [14]. Desolder
one side of L19, the side closest to the brown 7 pin connector. Now bend
the loose end of L19 in the direction of L23, and solder them together
[15]. Because one end
of L19 has been desoldered, a free hole remains. Solder a 4K7 resistor
in this free hole [12].
The other side of the 4K7 resistor is connected to the node of the 1N4148
anode and the 1 nF ceramic condensator [11].
Explanation: Usually the MD59LS transmits by applying a voltage to the
21.4 MHz crystal oscillator. The same oscillator is being modulated with
the 9K6 packet signal. It appeared that the first 50 ms the oscillator
couldn't be modulated well enough, which resulted in high tx-delays. PA3EKO
had the following idea: Don't remove the voltage during reception. Problem:
The receiver hears the 21.4 MHz oscillator during reception. So let the
oscillation stop during reception, without removing the voltage. During
reception diode 1N4148 conducts. Then the 1 nF ceramic condensator becomes
connected to the emitter of the oscillator transistor Q6, which stops the
oscillation. During tx this voltage is removed which results in a very
fast packet transceiver that can be modulated within 10 ms after keying
it.
|
... |
|
| ... |
Set
the local oscillator (LO) frequency using the dipswitches on the controller
board. Dipswitch SW1 is for MHz, SW2 for 12.5 kHz. Mf for both tx and rx
is 21.4 MHz.
Example:
The working frequency should be 430.6625 MHz. This means the LO should
be at 430.6625 + 21.4 = 452.0625 MHz. So MHz is 452, and number of times
12.5 kHz is 5 ( 5 times 12.5 kHz equals 62.5 kHz). SW1 already has a preset
of 384. So set SW1 to 452 - 384 = 68. Set SW2 to 5. To do so, close switches
64 and 4 of SW1 (together 68), close switches 4 and 1 (together 5) of SW2.
The
original DIN connector is used for both packet modem and voltage.
|
... |
|
